“One of the most common ‘under the skin’ lumps is called a lipoma, or fatty tumor, which is typically not cancerous,” Golden tells The Dodo. “Lipomas tend to show up on middle-aged to older dogs of any breed, although large breed dogs and overweight dogs are more prone to them.”
To identify a lipoma, the lump will feel “soft and movable” under the skin, notes PetMD. Often dogs develop lipomas on their bellies, though these lumps can appear anywhere. Lipomas typically will not bother your dog or require treatment unless they impede his movement. If your dog gets one in a sensitive area, like under the front leg, it may have to be removed by a vet, Golden explains.
While lipomas are typically benign, it is recommended that any mass be examined by your vet.
“Unless you’re sure about the cause of a lump or bump, bring your dog in for an exam,” Golden says. “Fast growth or sudden appearance, swelling, color change, pus or changes in your dog's behavior are all reasons to make a vet appointment right away.”